The present invention relates to an image-pickup device which picks up an image by using a solid-image pickup element, a defective-pixel-correction device provided in the image-pickup device, and a defective-pixel correction method, and particularly relates to an image-pickup device using a solid-image pickup element which can select a reading mode wherein signals of a plurality of pixels area added to one another, a defective-pixel-correction device provided in the image-pickup device, and another defective-pixel correction method.
Usually, a solid-image-pickup element installed in a digital-still camera, a digital-video camera, and so forth often includes a defective pixel which occurs by various causes including the occurrence of a dark current, a photodiode abnormality, and so forth. The defective pixel outputs a signal on an abnormal level. In the past, therefore, a known image-pickup device corrects an output signal of the defective pixel according to the defect degree, so as to prevent the quality of an image from being deteriorated. For example, the known image-pickup device detects information about the position of the defective pixel and the defect degree and stores the information into a memory. When photographing is performed, the known image-pickup device interpolates the defective-pixel signal by using signals of pixels provided around the defective pixel on the basis of the stored information.
In recent years, the number of pixels provided in image-pickup elements has been on the increase. However, there has been a demand for decreasing a drive frequency of the image-pickup element as much as possible. Further, there has been a demand for picking up an image with a screen rate higher than in an ordinary case, as an additional function of the image-pickup device. Due to the above-described demands, there have been methods including a method for adding signals of the plurality of pixels corresponding to filters of the same color to one another on a circuit of the image-pickup element, the same-color filters being provided on the image-pickup element, and reading the added signals, and a method for thinning out part of the pixels and reading the pixel signals. Further, in recent years, the use of XY-scan image sensors including a complementary-metal-oxide-semiconductor (CMOS) image sensor or the like is on the increase, where the XY-scan image sensors is configured, so as to easily perform the above-described reading methods.
Here, defective-pixel detection and correction performed by an image-pickup device having the above-described image-pickup element wherein pixels are added and/or thinned out will be described. If the above-described pixel addition and/or the above-described pixel thinning is performed while the defective pixel is detected, and the defective pixel is corrected by using information about the detected defective pixel, the same pixel addition and pixel thinning as those performed when the defective pixel is detected should be performed. However, if an image-pickup device can switch between modes, so as to determine whether or not the pixel addition and/or the pixel thinning should be performed, and switch among pixel-addition methods and pixel-thinning methods that are performed according to a plurality of reading patterns, and if the image-pickup device detects a defective pixel in only one reading state, it becomes difficult to achieve the same reading state as that when the defective pixel is detected while the defective correction is performed. In that case, the address of the defective pixel, the address having been stored when the defective pixel is detected, does not correspond to the arrangement of pixels provided on the image-pickup element when the defective pixel is corrected. Subsequently, it becomes difficult to correct the defective pixel in an appropriate manner.
Further, there is a known technology relating to the present invention, where the technology achieves an image-pickup device including an image-pickup element so that an image signal inverted vertically and/or laterally is output from the image-pickup element. In the above-described image-pickup device, it is determined whether or not the image signal is inverted vertically and/or laterally during a defective pixel is corrected. Then, the address of defective-pixel information stored in a memory is converted according to the determination result, and the defective pixel is corrected by using the converted defective-pixel information. The above-described technology is disclosed in Japanese Unexamined Patent Application Publication No. 2003-163842 (refer to paragraphs [0016] to [0019] and FIG. 3).
As has been described, where a defective pixel is detected only in a single reading pattern in an image-pickup device that can select patterns of reading a pixel signal from an image-pickup element, it is difficult to correct the defective pixel on the basis of image signals obtained according to all of the reading patterns by using the detection result, as it is. Thus, the known image-pickup device has no function of selecting a reading pattern, so that the reading state corresponding to the time where the defective pixel is detected is not different from that corresponding to the time where the defective pixel is corrected. Therefore, the above-described problem does not occur. In the future, however, reading patterns wherein various methods for adding and/or thinning pixels are performed may be provided, so as to increase the number of pixels of the image-pickup element and/or generate an added value of the image-pickup element. Therefore, the above-described problem should be solved.
For solving the above-described problem, a defective pixel may be detected in every reading pattern and information about the detection result may be stored in a memory. Further, when the defective pixel is corrected, the defective-pixel information corresponding to a reading pattern selected at that time may be used. According to the above-described method, however, the detection-result memory requires record areas of the same number as that of selectable reading patterns, which increases the circuit size and the manufacturing cost. Further, the steps of detecting the defective pixel become complicated. For example, the defective-pixel detection is usually performed during the product shipment. According to the above-described method, the number of steps performed, so as to detect the defective pixel, increases and the manufacturing efficiency decreases.